1. Field of the Invention
This invention relates to an sputtering deposition equipment used in semiconductor fabrication, and more particularly to an anti-microleakage apparatus used in a sputtering deposition equipment in order to prevent microleakage from occurring.
2. Description of Related Art
In semiconductor fabrication, a metal-oxide semiconductor (MOS) structure is usually composed of multiple thin layers, each of which includes different material and thickness. A technology to form these thin layers is so called thin film deposition and thin film growth. The word of deposition means that the formation of the thin layers consumes no material on substrate, which may include only the primary semiconductor substrate or a few more films, such as a silicon oxide layer, already formed.
About the deposition technology, it can be traced back to the early stage that was evaporation deposition. Nowadays, it has been developed into two categories: physical vapor deposition (PVD) and chemical vapor deposition (CVD). The words of physical and chemical characterize the technologies by words themselves.
The PVD technology further includes evaporation deposition and sputtering deposition. The evaporation deposition includes heating up an evaporative material to form a saturated vapor with high temperature and depositing the saturated vapor onto a wafer. The sputtering deposition includes producing plasma ions by bombarding a target, which also serves as an electrode and includes the desired material to be deposited, and drifting ions onto a wafer, which is put on the other electrode to attract plasma ions.
The evaporation deposition can only be used for a material with low melting point, such as aluminum so that the PVD process usually employs sputtering deposition. FIG. 1, is a cross-sectional view of a conventional sputtering deposition equipment. In FIG. 1, a sputtering deposition equipment includes a cryo-pump 10, a process chamber 12, a bellows line, a gate valve 16, and a heater 18.
During performing a metal sputtering deposition process, a tolerance of impurity, such as O.sub.2 or H.sub.2 O, is poor so that the process chamber 12 is vacuumed by the cryo-pump 10 to clear out all residual oxidizer gas before sputtering process is performed. This pressure before sputtering process is called base pressure, which usually is about 10.sup.-7 -10.sup.-8 torrs.
After the process chamber 12 is vacuumed, a gas is flushed in from the bellows line 14. A heavier noble gas, such as argon, is preferred. In addition, in order to have a better step coverage performance for a metal layer, it is necessary to heat up the wafer to increase mobility of the metal atoms on the wafer surface. The heater 18 is used for this purpose to obtain a temperature of 350.degree. C.-400.degree. C. The heater 18 can move up and sown in accordance with the bellows line 14, which is extendable.
However, since the bellows line 14 is wrapped by steel lines shown in cross mark, when the bellows line 14 moves up and down, a friction from the steel lines naturally occurs. Particularly, the friction may cause a microleakage at the junction between the bellows line 14 and the heater 18. The microleakage can affect the inner pressure of the process chamber 12. A pressure of 10.sup.-8 torrs may not be normally maintained. If a large variance occurs, such as over 10.sup.-5 torrs, the gate valve 16 then automatically closes and results in a stop of the sputtering process. If the microleakage occurs, a pressure of, for example, 10.sup.-6 torrs may exist. At this pressure level, the sputtering deposition equipment does not trigger a warning to an operator, the abnormal pressure status leaves unnoted. It can cause a failure of a large number of wafers in processing.
In conclusion of above descriptions, microleakage in the conventional sputtering deposition equipment may occur and leave it unnoted. This can cause a failure of a large number of wafers in processing.